Our sea level is rising at an increased rate, and the primary cause is higher temperatures.

As the temperature rises, the water gets hotter. As it heats up, the water expands, with warmer oceans taking up more space. Higher temperatures also cause melting glaciers and ice caps to melt faster, putting more water into the ocean.

Trends

Global average sea level rose by 0.18 centimetres per year from 1961 to 2003. The total rise from 1901 to 2010 was 19 centimetres, which is larger than the average rate during the previous 2000 years.

Around Australia, and in the Great Barrier Reef, the fastest rates of sea level rise are in the north.

Extreme sea level events (storm-driven waves and surge) also became about three times more frequent during the 20th century.

The Intergovernmental Panel on Climate Change projects that global sea levels will rise by around 26 to 29 centimetres by 2030, and by around 47 to 62 centimetres by 2080.

Effects

Sea level is important in determining the distribution of species and habitats, and affects foraging and breeding activities of many species.

Over the past 100,000 years, sea levels have risen and fallen many times, shifting where reefs grow on the continental shelf. Sea levels on the Great Barrier Reef have already risen by approximately 3mm per year since 1991.

Since 1959, records of sea levels for Townsville, in north Queensland, show an average increase of 1.2mm per year. However, the rate of increase may be accelerating, with records of sea levels at Cape Ferguson near Townsville showing an average increase of 2.9mm every year between 1991 and 2006.

This sea level change is considered small in the context of the Great Barrier Reef’s geological history; however, it’s believed sea levels had been very constant for the past 6000 years.

Most reefs in the region will probably be able to accommodate the current rate of sea level increase as the maximum rate of reef growth is about twice this.

However, sea level rise is predicted to increase at a higher rate, and coral reef growth may not be able to keep pace. The shape and existence of some coastlines, cays and islands may also be affected.

Because much of the land adjacent to the Great Barrier Reef is low-lying, small changes in sea level will mean greater erosion and land inundation. This will cause significant changes in tidal habitats, such as mangroves, and move saltwater into low-lying freshwater habitats. This will have flow-on effects for juvenile fish that use these habitats for protection and food resources.

Turtle and seabird nesting beaches are particularly vulnerable to rising sea levels, as this would exacerbate beach erosion and flood nests.